1. Field of Invention
The present invention relates to a sprung mass estimating apparatus for estimating the mass of a sprung member of a vehicle.
2. Description of Related Art
Related conventional apparatuses are described in, for example, Japanese Utility Model Application Laid-Open No. HEI 7-27907 and Japanese Patent Application Laid-Open No. HEI 1-293211. The apparatuses detect an air pressure in a pneumatic spring mechanism, and estimate the sprung mass (movable load) in the pneumatic spring mechanism from the detected air pressure, based on the fact that the air pressure is proportional to the sprung mass in the mechanism. In accordance with the estimated sprung mass, the apparatuses change the damping force characteristic of a damping force generating mechanism, or adjust the amount of air supplied into or discharged from the pneumatic spring mechanism. Japanese Patent Application Laid-Open No. HEI 8-304154, as for example, discloses a technology that detects a sprung mass (movable load) based on the amount of displacement of a spring disposed between a vehicle body and an axle, and displays the sprung mass on a display device provided near a driver's seat.
The above-described conventional apparatuses are able to accurately detect the sprung mass if the sprung member (vehicle body) is not oscillating, for example, when the vehicle remains stopped. However, when the vehicle is moving, that is, when the sprung member is oscillating, the air pressure in the pneumatic spring mechanism fluctuates, so that the conventional apparatuses cannot accurately detect the sprung mass. Moreover, the related technology employing a pneumatic spring mechanism as described above, in particular, requires a dedicated pressure sensor provided in the air spring mechanism.